netdev - Re: nf_conntrack: Infoleak via CTA_ID and CTA_EXPECT

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Date:   Fri, 30 Jun 2017 22:23:24 +0200
From:   Richard Weinberger <richard@....at>
To:     Florian Westphal <fw@...len.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        David Miller <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        David Gstir <david@...ma-star.at>, kaber@...sh.net,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: Re: nf_conntrack: Infoleak via CTA_ID and CTA_EXPECT_ID

Florian,

Am 30.06.2017 um 21:55 schrieb Florian Westphal:
>>> Why not use a hash of the address?
>>
>> Would also work. Or xor it with a random number.
>>
>> On the other hand, for user space it would be more useful when the conntrack id
>> does not repeat that often. That's why I favor the good old counter method.
>> Currently the conntrack id is reused very fast.
>> e.g. in one of our applications we use the conntack id via NFQUEUE and watch the
>> destroy events via conntrack. It happens regularly that a new connection has the
>> same id than a different connection we saw some moments before, before we receive
>> the destroy event from the conntrack socket.
> 
> Perhaps we can place that in a new extension (its not needed in any
> fastpath ops)?

To get rid of the infoleak we have to re-introduce the id field in struct nf_conn
and struct nf_conntrack_expect.
Otherwise have nothing to compare against in the conntrack/expect remove case.

So the only question is what to store, IMHO a counter that can wrap around is the
cheapest method and would also not harm the fast-path.

Thanks,
//richard